the answer is that canada is the part of british north america that wanted to stay in the british empire. it's not an "artificially drawn line", it's a line that was drawn by canadians and defended with our lives. canadians were on the other side of the american revolution; in fact, the country was largely unpopulated before 1776 (there were francophones and natives, but the population density was extremely low), and was populated primarily by british loyalists fleeing from the american revolution, and moving further back behind british lines that could be better defended.
one of the major things that the united states was founded over was the concept of property rights. to this day, there is really no clearly discernible concept of property rights in canadian law.
nowadays, canadians aren't likely to pick up their muskets to fight off americans that want to assert what many canadians think is the depraved and stupid concept of property rights, but we do like our health care system and we don't like gun ownership very much.
there are similarities, and i wonder if trudeau didn't say something stupid to trump when he went to florida that has generated this mess, but we are not americans and we have dramatic cultural differences that are not going to get smoothed over very easily. america should not push us too far. it might not like the result.
we are very much to the united states as the scots are to the brits.
america may take our lives, but they'll never take our freedom.