D1's response:
There's a few companies to choose between, I think True Traveller and Alpha are the main ones. Things to look out for are whether you're limited on the number of days you're allowed to go home for whilst still being covered, excess, customer service etc. I went with True Traveller after reading very good reviews. It's not cheap but obviously insurance only feels like good value if you end up needing it.
There's criteria on the Canadian immigration website about what the insurance needs to cover, but the one that I remember is repatriation in the case of serious injury/illness or death. Once you've been working FT in BC for 3 months you become eligible for provincial healthcare coverage (for $75 per month), so the insurance is really to cover you for the first few months and if anything really big happens.
The visa you get given at the border will be as long as your insurance policy ie even if you're entitled to a 2 year visa, if you only have 1 year of insurance you'll be given a 1 year visa.
Hope that answers the question and is helpful?