If you were on prepaid, you'll have to start everything again from scratch with a new SIM and new number. Prepaid accounts are wiped from the system after 90 days of inactivity.
If you were on postpaid and did not cancel before you left, well, unless you paid all your monthly bills in advance, you'll be in for quite the shock.
If you have past due amounts, they likely have gone to collections by now, which will badly hurt your credit rating, likely wiping away any chance you might have had to get another plan with Koodo (or any other cell provider, really).
So, first thing first, you'll likely have to pay all those past due amounts first.
Then, the reps will take it from there about getting a new plan (or not).
If you kept paying, however, everything should be fine and dandy and you can disregard everything I wrote above.