I've also been looking at this for a future purchase (potentially save 000s).
Look at the Registrar of Imported Vehicles web site:
http://www.riv.ca/MakeAnRIVPayment.aspxFor non-propelled (ie. trailer), it's basically a flat fee of around $200 and then you pay the GST at the border. You have to get it "safetied", which in Manitoba means taking it to a Canadian Tire so they can look at the tires and say "OK" (rubber stamp).
Also, in Manitoba, you pay the PST when you register and insurance it.
I've known many people that do this and it's very straightforward.
Derek