lawl. But seriously, the Canadian Senate is our version of the UK House of Lords. They are there to balance the common parliament in the same way that the Governor General balances both houses. As for the question of what happens if the Governor General goes crazy and acts against the public interest, along with the government (both houses)...we're fucked. There can be no guarantees in politics and government, but there can be steps that will reduce the chance of rash decision making. Like I've said somewhere else, its the reason for an entrenched constitution and a charter of rights and freedoms. Of course, any law (including entrenched law) can be changed through an amending formula, but it is so difficult to do that any change must be well thought out and heavily supported.
I think that the Queen of Canada also provides a key function that non-commonwealth states (e.g. the US) are lacking: honour and pageantry. The commonwealth (and particularly Canada's) system of honours and formality provides a sense of dignity to the realm. I think it is an excellent balance of the old school where honour was a real thing that determined the order of society and the new school of equality of opportunity.