It has been mentioned in this thread but I think it's worth saying it again in view of the comments..'if it's okay where you live, it's okay in other places too'...and I think that is accurate, however...for those that double tow, in BC, for certain, that is NOT allowed. And yes, there are those souls that have gotten a goodly number of miles into the province only to get pulled over and forced to drop one of the towes and make other arrangements.
You can double tow in Alberta.
http://www.transportation.alberta.ca/Content/docType41/Production/recvehtowguide.pdfGary Haupt