One flavouring used by many people in the Eastern Woodlands and Great Lakes traditionally is maple syrup. Indigenous peoples in those areas invented the technology for taking maple sap and turning it into syrup. There has been some debate among archaeologists about to what extent this maple syrup was further refined into maple sugar in pre-Columbian times. Either way though, maple syrup was definitely used to flavour foods by many different peoples of the region.

To make maple syrup, you collect sap from sugar maple trees and evaporate it until it has the desired percentage of water content. Sap has to be collected during late winter and early spring due to the day and night temperatures required for ideal sap conditions. The importance of collecting maple sap at this time of the year is reflected in the month names of various Indigenous languages. The Western Dialect of the Ojibwe language calls April Iskigamizige-giziis, or Sugarbushing Moon; the Menominee call April Sūpomāhkwan-kēsoq, or Sugar Making Moon.

The beginning of the sugaring season is often marked by special ceremonies such as a "first tap" festival, which marks the transition from winter to spring. Among the Ojibwe, the first tap festival involves taking old sugar from last season and new sugar from this season and pressing them together. A medicine man says a prayer of thanks over the sugar and then distributes it to community members. Similar festivals happened all over the northeastern part of the continent during the springtime. Although these ceremonies were outlawed in Canada by the Indian Act, they have survived colonization in many places. Indian agents would lock up the longhouses during the maple season to prevent people from processing sap, but the people would go behind their backs and tap the trees anyway, risking prison time to do so. Residential schools and the seizure of Native lands also damaged sugarmaking traditions among Native peoples. In spite of these obstacles, sugarmaking ceremonies persist to this day and remain an important part of the seasonal cycle of celebrations in many communities.

Maple syrup is used as seasoning in a lot of traditional recipes. Here's a few examples from the Traditional Foods Toolkit from the Wisconsin Department of Public Instruction:

The Menominee cook wild rice with deer broth, pork, or butter, and season with maple sugar. The Ojibwe [...] cook [wild rice] with deer fat and maple sugar. The Potawatomi use maple sugar when making wild rice pudding or preparing it with wild fowl or game.

While pork and butter are not pre-Columbian ingredients, the rest gives you an idea of some recipes that maple syrup was traditionally used in. The document linked above gives the recipes of some maple-seasoned dishes, such as maple squash bake or wild rice and oatmeal bake. It was used in flavouring and preserving meats like venison too. Maple syrup was also used medicinally, mixed into water and drunk to help with health issues such as heart and digestive problems. They were thought to be especially helpful when eaten during winter, so maple products were preserved for this purpose.

During the early colonial period, maple products were popular trade goods with the French and English. Maple products were so popular with Europeans that Native production intensified during this period. For example, in the 19th century, the Indigenous community of Manitoulin Island exported over half a million pounds of maple sugar every year. The Europeans introduced metal technology which made it possible to produce more syrup and to refine it into sugar.

There are some great oral traditions about the origins of maple syrup processing among various Native groups. Here's an Ojibwe story:

A very long time ago, when the world was new, Gitchee Manitou made things so that life was very easy for the people. There was plenty of game and the weather was always good and the maple trees were filled with thick sweet syrup. Whenever anyone wanted to get maple syrup from the trees, all they had to do was break off a twig and collect it as it dripped out.

One day, Manabozho went walking around. "I think I'll go see how my friends the Anishinabe are doing," he said. So, he went to a village of Indian people. But, there was no one around. So, Manbozho looked for the people. They were not fishing in the streams or the lake. They were not working in the fields hoeing their crops. They were not gathering berries. Finally, he found them. They were in the grove of maple trees near the village. They were just lying on their backs with their mouths open, letting maple syrup drip into their mouths.

"This will NOT do!" Manabozho said. "My people are all going to be fat and lazy if they keep on living this way."

So, Manabozho went down to the river. He took with him a big basket he had made of birch bark. With this basket, he brought back many buckets of water. He went to the top of the maple trees and poured water in, so that it thinned out the syrup. Now, thick maple syrup no longer dripped out of the broken twigs. Now what came out was thin and watery and just barely sweet to the taste.

"This is how it will be from now on," Manabozho said. "No longer will syrup drip from the maple trees. Now there will only be this watery sap. When people want to make maple syrup they will have to gather many buckets full of the sap in a birch bark basket like mine. They will have to gather wood and make fires so they can heat stones to drop into the baskets. They will have to boil the water with the heated stones for a long time to make even a little maple syrup. Then my people will no longer grow fat and lazy. Then they will appreciate this maple syrup Gitchee Manitou made available to them. Not only that, this sap will drip only from the trees at a certain time of the year. Then it will not keep people from hunting and fishing and gathering and hoeing in the fields. This is how it is going to be," Manabozho said.

And, that is how it is to this day.

Here are some notes I have on the Pacific Northwest. The natives of the Southern Northwest Coast Culture Area (Oregon and California) used a variety of materials to season food. Angelica california (commonly wild ginger) root was dried, ground and sprinkled on other foods. Angelica was a plant related to the supernatural and was frequently burned and eaten/chewed during religious ceremonies, but also routinely used as a spice. Sea weed (red algae and others) was used after drying. Peppercorns and leaves of California Bay laurel were ground and used on other dishes. Often berries and other plant fruits that had distinctive flavors like manzanita, elderberry and salal were used both dried and fresh as condiments.

In the Puget Sound area rose hips were used to season salmon eggs eaten raw. Berry shoots from salmon berries and trailing blackberries harvested early in the spring were used fresh on other foods and added a tart, sweet flavor. And probably the most well known seasoning agent was the aged oil extracted from fish, most commonly eulachon oil or grease that was used as a dip for smoked fish and other foods, as well as eaten alone.

This is way out of my area of knowledge, but I'm pretty sure there is a lot of documentation of for you in the Pacific Northwest ethnobotany arena. Here is a couple that I know of.

Ethnobotany of Western Washington, Erna Gunther, 1945…1981, University of Washington Press

Food Plants of British Columbia Indians, Part 1/Coastal Peoples, Nancy J. Turner, 1975, Province of British Columbia Department of Recreation and Conservation

Indian Tribes of California. 1877 Contributions to North American Ethnology Vol. 3, Dept. of Interior. Stephen Powers