Having had a good look through many posts here I have noticed a couple of different practises regarding underlayment for 3/4" strip t&g hardwood floor for northern US and sourthern ont regions. It seems many suggest 15lb felt roofing paper or wax paper. Whats are your thoughts on one vs the other?

Well, now. That is a very regional thing. 15 lb is commonly (but not exclusively) used in the U.S. and Quebec areas. Wax paper is the product most used in Ontario (we are collectively very cheap doncha know). Being the technical advisor for the company I work for, I was given the task of finding something that would be most ideal to protect the floor from moisture penetration from below, without taking anything else into consideration. Two years ago the result of my testing was concluded and we started using a product called V-lok on all main floor installations. Prior to this, our service dept. was deluged by customer calls about floors cupping, squeaking, etc. during the summer months. This was in large part, due to the speed at which houses are built in our area : corn field today, occupied house 8 weeks later.
Since then, virtually all complaints regarding cupped floors have ceased. Of course, since there hasn't been any lab testing done, I cannot say if there could be any long term detrimental effects caused by this product, but Im guessing not. Then again I live right near a casino so am used to gambling, lol.
As a note to the American floor experts on here, the type of house construction most commonly found here are brick veneer cladding over 2 by 6 framed walls restng on concrete foundation walls with full height basements which are usually left unfinished for the first 2-3 years, if ever.