Since this thread is still live, I feel like it's worth throwing an unpopular opinion out there for discussion:
John A. MacDonald wasn't particularly important. Most Canadians are just so uninformed about Canadian history and so inured and inundated with American history that there's this impulse to transform John A. MacDonald into a sort of Canadian version of George Washington. I would wager that more than 95% of Canadians couldn't name more than three people in this painting without googling it:
In the absence of a solid understanding of Canadian history, it's easy (and tempting) to want to assign personal/human agency to historical events. It makes understanding history much easier when the answer is that x, y or z happened because a "great man" did it. That's the only explanation I can come up with for how people can claim with a straight face that Canada (or some aspect of Canada) only exists by dint of John A.'s brilliance or greatness.
In reality John A. was a petty drunk who happened to be extremely fortunate in his political life and extremely unfortunate in his private life. His three principal professional accomplishments were (1) being in the right place at the right time to secure leadership of the one federal party that was all-but-guaranteed to win him political power, (2) being corrupt enough to keep power once he had it, and (3) hanging Louis Riel.
Now my bit of personal speculation: I would wager that if we could hop into a time machine and hurl John A., in his drunk stupor, in front of a racing carriage to his death, and then come back to the present time, we'd see way less that would have changed than is commonly assumed. And what little would have changed maybe might have changed for the better.