Can only speak for Canada, but as colonists pushed westward across the plains, the spread of diseases such as smallpox, aided in the colonization process. This alone probably crippled indigenous communities’ ability to resist. My chronology might be off, but soon after colonists made contact with the Pacific colonies, treaties were made across the country under the assumption that the native population would have some sort of peace and regain autonomy over their land. But colonialism didn’t stop with the treaties. The introduction of “Residential Schools” affected several generations of indigenous people by attempting to white wash children so they could eventually enter mainstream (ie. white) society “civilized”. Don’t get me wrong, it’s not like the native population just “gave up.” I think it’s more that they simply didn’t have the means to continue to resist. As more European colonists came to Canada, continuing their way of life just was not realistic.

The vast majority of aboriginal deaths in North America occurred from disease, not warfare. There were massacres, but they pale in comparison to the toll that disease and starvation inflicted on the natives.

It's perceived of as more peaceful in Canada because Canadian law enshrined the Royal Proclamation 1763 that forced the government to negotiate land claims and treaties with native tribes *before* colonizing the land. In the US they didn't have that - speculators and settlers would often survey out an area, settle it, fight with natives, then call in the army to defend the settlers.