Also, you remember how Thatcher was deposed by her party MPs in 1990. Could that happen in Canada? or are modern Canadian PMs too well entrenched for that to happen in Ottawa? Both governments use the Westminster system but no two democracies are perfectly alike.
There is certainly a lot of entrenchment involved.
MPs can (in theory) always vote any way they chose at any time. (The prime minister does have the ability to kick people out of caucus and keep them from running for the party in future elections, so voting against the party is a rather significant step, and not one to be taken lightly.)
If a prime minister IS found to be abusing power, it would be hoped that MPs from their own party would vote against the party in a "confidence motion". (Basically a special resolution, and/or any bill that involved finances.) This would mean they would be 'kicked out' of power, and the Governor General would either call an election, or invite one of the other parties a chance to form the government.
I think the big difference between the Canadian and U.K. systems is that Canada tends to enforce party discipline a lot more often (i.e. "vote the way the rest of the party is, or we kick you out"), whereas the U.K. gives its MPs more flexibility to vote how they want (unless its on a matter of confidence, and/or related to a campaign promise.)