Shipping tobacco from outside Canada to Canada is perfectly legal. Canada Customs may assess the duties and taxes, IF they feel the urge, to do so.
It boils down to a few things.
#1 - declaration value. If the value is high enough that it is worth collecting the assessed fees, no matter what the item might be, they will assess and charge.
#2 - accurate declaration. If Canada Customs thinks the contents are not as portrayed, in most cases they will open.
#3 - weight. A small package with a lower value will in many cases " slide" through unmolested. Even tobacco. The $30.00 US declared value for 3 x 50 gram tins, is not worth the amount of paper work / effort to collect the duties / fees etc. 8 oz on the other hand, even if declared at correct value is worth the effort to collect.
The way duties and taxes are assessed is on value and weight for tobacco products. Even low value but higher weights, can mean fees being assessed.
ALL the above goes out the window, depending on how diligent the customs official is about doing their job. Some will go after even 50 grams, and some will let higher weights slide through. It's a roll of the dice every time.
Regards
Michael J. Glukler