Some inscrutable calculus involving party, policy, and personal character.
There are famous Canadian politicians, like the late Ed Broadbent, whom I personally admire for their integrity and patriotism, but couldn't vote for because of their affiliation (i.e. he was the former leader of the New Democratic Party, which was hardcore socialist).
On the other hand, though I'm a nominal Conservative voter, had I been able to vote when I was still living at home, I'd have had no qualms voting for their longtime Liberal MP. He was effective and personally nally a decent guy.
Though I wouldn't vote for the same guy today because under Justin Trudeau, the Liberals have drifted way too far to the left.
As to the question of who is "morally upright" enough to deserve my vote, of course no one is perfect. But you have to admit that "more than Donald Trump" is a pretty low bar.