i have always used Nirvana seeds (directly, and through seedsman). reputable and been around a long time. great consistent genetics. im sure there are many other great producers too.
Some Canadians don't like much of what seedsman, attitude, herbies and so on offer. Yes they have loads to offer but there is a lot of garbage. The US banks generally have less variety of breeders but most of them offer the new-new, so if you're chasing that then those would be the place to look.
There are other reasons but i am too lazy to.rype them out but it is well documented on here.