Canada is very useful and helpful (from a historical standpoint) as they send troops to both Britain and the USA ( United States of America) during WW1(world war 1), WW2(world war 2), And the cold war. Plus unlike the USA, They never lost a war. And yes their equipment is a bit out-dated, But their training along with their anti-terrorist group is some of the best in the world and can rival the USA. (not saying they will)
First of all, Canada is very useful when it comes to the Military, their JTF-2 Tier One Special Forces group has been a valuable asset to the United States in Joint raids against terror groups. Although their Infantry is not well trained and their equipment is slightly outdated, they are still very valuable to us as a nation.
Since Canadians are so polite and abhor conflict, they would be unwilling to fight anybody. Sure we could count on them to not invade directly, but any enemy that offers them any kind of gift, and asks nice enough, is bound to be allowed through Canada without resistance, perhaps even receiving help and gifts.