Most humidors are lined with Spanish cedar but are not built in whole with it simply because it is kind of boring looking and the are much prettier woods out there. You can find Spanish cedar at many online wood stores in Canada, or you might check out Windsor Plywood. Their prices are usually a bit more expensive, but factoring the small quantity you will need and the convenience of a store front, I would probably suggest starting there.
As for plans, if you are already somewhat woodworking proficient, it isn't difficult and is not really any different that building any box like a jewelry box or the like, except with a few more details, but if you like to have step by step instructions, online there are a wealth of free plans out there.
This one is decent... Just alter measurements to scale if you want something bigger or smaller.
http://www.taunton.com/finewoodworki...ee/humidor.pdf