I know in Canada you are much more limited in how many guns you can own, and how often and where you can shoot. It certainly makes selection of your gun much more important, it probably being your only one. Generally speaking, the further north you go, the larger the species tends to be, meaning that up in Canada, like in the northern states, your deer can get pretty big. This means you want to keep up in a larger caliber- at least .30, stay away from the lighter .243s, etc.
Calibers are confusing. Generally speaking in the given caliber designation, it gives the caliber in hundredths of an inch, thus .22 is twenty two hundredths, .308 three hundred and eight hundreths of an inch, .45...etc.
This is only part of the story though. You can have many rounds in approx. the same caliber but different powers. The 30-30 is a very much lighter round (but adequate for deer) than the 30-06, which isnt as powerful as the .300 win mag, etc.
You cant go wrong as others have suggested by leaning toward a round such as the .270, 30.06, or .308. All will do whatever you ask of them if aimed properly. I prefer the .308, as it has essentially the same ballistics as both the older .270 and 30.06, but in a shorter and lighter action.
The best source for you is to simply read, read, read. These forums are a quick way to get a small snapshot of information, but no excuse for not hitting the books.Several excellent books on deer hunting are "Hunting Big Woods Bucks, by Hal Blood, and "How to Bag the Biggest Buck of Your Life" by Larry Benoit.
Both these books are about hunting the northern woods, and contain gobs of excellent information. Remember, alot of hunting is getting out there, scouting, and woodsmanship. Know your woods basics- safety, direction finding, how to dress, knife use, etc. It is alot to learn, and the basics that make the hunter are often overlooked. The pulling of the trigger only take a moment.
You mentioned you already had a pellet gun, and that is excellent. Never under estimate the importance of being able to practice marksmanship frequently. Good luck