"I am going to Canada this year."
It means the same thing in this case. Tsumori is used when you know for sure you're going.
It would be nice for new learners though if Duolingo made an effort to show the difference between Verb and Verb+つもり
Not sure that's right. You "intend" to go isn't the same as definately going. I had heard "yotei suru" (to plan / to schedule / to arrange) is stronger.
Yes, I believe it makes sense because the event is in the future, so it's technically just a "plan". And of course there's no future tense.
行く is the plain form and should be used with つもり and other such constructs.