Well, I work for one of the shipping companies mentioned. The way that the packages come are 10ft piled high boxes, It depends who is "packing" the trailer to its destination. It could have any amount of weight on it, so I would discourage shipping as a guitar is a very fragile instrument. The main worry is the transportation between the center in one city, to the center in another city. Once it has done that, the worst part is over.
If you do decide to ship it, label the package with "fragile" all over. You can never have too many warnings. Also, request a signature. Some require some more expense for signatures. As far as i know, most of the companies ship quite similarly. UPS ships up to 150 lbs, same with Fedex. According to
http://www.canadapost.ca/tools/pg/ma...expparus-e.asp the weight max is 30lbs, so that might be your safest bet. If i was to ship a guitar through UPS or Fedex, I would create a make-shift crate out of plywood to entirely cover the whole guitar.