50-100 turns safety from no surprise war? Are you talking standard speed? We have been playing different games then. I get DOWed a formal war (joint war is a formal war) before that on epic in most of my games. I think that Firaxis wants Canada to be immune to attacks in single player for some time, so they won‘t program a specific AI behavior when facing Canada. However, something like builder/settler/settler is still not a sensible build order. I‘ll probably just start builder/slinger/slinger/slinger/warrior just as with any other civ. Only going to change if I have no barb camp nearby (which I won‘t know before the first slinger is out
).
As to the AI declaring formal wars alone early, they rarely do in my games. In the later game they use the colonial CB, however.

As to the AI declaring formal wars alone early, they rarely do in my games. In the later game they use the colonial CB, however.