Polynesian technology was only "limited" in the sense of not having access to a lot of modern ship-building materials. In design, they were extremely complex. Captain Cook observed that the Polynesian canoes could run rings around his own ship. Some features of Micronesian/Polynesian canoes were not invented in Europe until the renaissance. Also, perhaps the word "canoe" is misleading to you, since you're picturing something like this. Some Polynesian canoes were longer than Cook's Endeavour. A Marshallese walap (lit. boat-big) could carry up to 50 people and took over a year to construct. The biggest Tongan war canoes could carry up to 100 people as well as the spoils from their many raids. Here is a photo of a 100ft Gilbertese barua and this is a Māori waka in action.

As for navigation, Polynesian and Micronesian navigational skills were the product of several thousand years of accumulated knowledge and experience. Several complimentary methods were used: reading swells, stars, clouds, bird migration patterns and more. These skills were normally passed down orally and through practise and demonstration. The Marshallese also made complex maps of three different types, the meddo, mattang and rebbilib which I believe were used as instructional aides, rather than being taken on the voyages themselves. I took two photos of various types of stick charts at the Alele Museum in Majuro. Finally, it's worth noting that although the modernisation has led to better construction materials, many of the sea-faring vessels still constructed today are of the same design (c.f. this photo I took in Jaluit atoll). In other parts of the Pacific, canoes are still made with traditional materials.

You should check out David Lewis' (1994) We, the Navigators: The ancient art of land-finding in the Pacific, which says everything I have just said and a lot more. It's a really fascinating book.