Complex sentence: There was a possibility the by-election will not be held because of a non-confidence vote the week prior, that would have toppled the government, sending Canadians to the polls, and would have superseded the by-election.
Split into simpler sentences: There was a possibility the by-election would not be held because of a non-confidence vote the week prior. The non-confidence vote would have toppled the government sending Canadians to the polls, which would have superseded the by-election.