definitely a matter of opinion...
I've only driven a 4th gen once. My impression of it compared to my 3rd gen was it has more power (V8), it drove like a larger vehicle (yes it is) and felt more refined and sophisticated-- more bells and whistles. (I prefer simpler-- less to go wrong!) AND here where you need to do the PROS and CONS! You now have to ask yourself what you want:
1) What's your budget?
2) Do you have room for 2 trucks and can you do some mechanical work yourself?
3) How much time are you willing to invest?
I love my 3rd gen, It has a great ride for a truck, it does what I need it to do, its not too bad on gas, its comfortable to drive, and I trust it to get me there.
You can have fun with what you have and with a few mods, it can be reasonably off-road capable (not that stock isnt already). However, if you want to get seriously off-road, compromises will have to be made, ie. trail handling or road handling, $$$, comfort, and the possibility of scrapes, bangs and dents.
If serious off-road is your thing, then picking up a 3rd gen is a great alternative. If you've been cruising this site, you"ll know that many members say that the 3rd gen is arguably the most reliable and durable 4Runner. They are highly mod-able with lots of options--- and they're plentiful. Yes, the initial outlay may set you back 5-10K depending on shape and year of the truck. Being in Ont., rust will be your greatest obstacle.
I've owned a couple of trucks and lots of cars and I can tell you that generally, the 3rd gen is one of the nicest vehicles I've worked on, with the exception of some of my very first cars(pre-polution controls), its well laid out and well engineered-- easier to work with, than most. You will have to do maintenance but most of it can be done in the driveway, parts are not outrageously expensive, and this truck is reliable. There is no wrong answer. It really is a question of your needs and wants! Good luck!!