Do you have a link that shows a sea can or shipping container can't handle Canadian snow loads?  I live in the north and have never seen a sea can leak or collapse.  Plus, I have found sources that state, "the roof is able to support an imposed load of a minimum of 330 lbs/sq. ft."

http://www.residentialshippingcontainerprimer.com/ISO%20Shipping%20Containers%20and%20Building%20Code%20Requirements%20

I am sure 330#/sq ft is more than ample for Canadian snow loads.  Although I may be wrong. 

As for heat transfer of metal, this can be easily dealt with with insulation.  I personally feel that these containers are an often overlooked, inexpensive and extremely robust building or building component.