The Conservative government would probably blame the zombie apocalypse on Liberal mismanagement they were only able to end 4 years ago, (a tragically small number) spend millions on a Royal Commission to study the extent of the issue to look smart, and then just do what the Americans are doing no matter how good or bad an an idea it is. They will then find a way to blame any casualties on the previous Liberal government. Michael Ignatieff and every provincial leader of the opposition would accuse the government of mismanaging the zombie threat no matter how well it does, and Elizabeth May will blame it on global warming and Stephen Harper's climate change in-action plan. A motion to declare war on the zombies would be passed quickly through the House of Commons, but more slowly through the Senate, as the Zombie Apocalypse may have reduced their ability to get their arthritis medication and hearing aid batteries. It will then go to the Governor-General, who will immediately sign it into law, and control of the crisis will be handed to the military, which means things will finally start to happen.
People would probably be ordered to go to their cabins or cottages (whatever you call them) immediately. This will spread everyone out of major cities and allow the army and reserves to mop up any remaining zombies, while some forces go to major cabin/cottage area's and start vaccinating people with the highly competant national vaccine manufacturing company creating millions of vaccines a day.
Assuming the threat is taken care of that swiftly, we then need to deal with the millions of Americans trying to escape the terribly managed threat south of the border because Republicans believe it's just as much a money making hoax as global warming. (It is really happening? Ok well, even if it is, it's not that bad, and it's partially a natural cycle anyway, these sorts of things happen all the time. And even if it is the giant threat zombie apocalypse alarmists make it out to be, the market should take care of it rather than giving into a foreign socialist scheme to take away American sovereignty and give it to third world nations. And if it really is that bad, there's really nothing we can do about it anyway.) The Conservatives would probably like to just deport them all and throw the infected out of helicopters, but the stability on the domestic front (AKA, the public aren't distracted) would prevent the Conservatives from showing all their teeth, and true desires, until they get a majority. Refugees from everywhere would be given food, shelter, vaccinations, and low-interest loans for those who can't afford what they are being given, as such would be the will of the Canadian people.
Stephen Harper would still use every free moment to plot a majority. Speaking of which, the vaccinations of many Opposition Members may accidentaly have had too much of the virus in it, and they simply became infected beyond hope, and had to be put down. Several by-elections are held in previously non-Conservative ridings, where millions of dollars are poured into each Conservatives election campaign as a $350 million election is held during a global zombie apocalypse. The people riot, AND THEN...
...
I have no idea. To hard to tell. Yep, that's how this entire theoretical ends.