Agreed with
zardoz that it is way easier to deal with a Canadian insurance provider when it comes to visitors insurance. As for which insurance plan to choose, there are quite a few options available on the market for people coming over to Canada.
I would suggest to take a look and compare different insurance plans before getting the policy to make sure that you are getting the best coverage for your budget. Policies from providers like Manulife, while well-known and provide sufficient medical emergency coverage, are a bit pricey on average. You might get similar coverage at a lower rate by going with a different insurer.
Just note that all insurance policies for visitors to Canada and new immigrants (which is the exact same product) will only cover medical emergency treatment for unexpected things like sickness and injury, while not providing any coverage whatsoever for routine check-ups, over-the-counter medications, continuation of an ongoing treatment and elective medical care procedures among other non-emergency care.
And yes, it is best if you get your insurance policy before leaving your home country and arriving in Canada so that you coverage, depending on the plan of your choice, start either on the date of your arrival in Canada or the date of your departure from your home country.
You will be able to get a personal quote as well as compare different options here -
Temporary Medical Insurance