William Hill is a good pick for a beginner. It's safe (it's a large, established bookmaker with 1500 outlets in the UK) with a simple interface. You can bet in CAD and they will pay winnings back to your credit card which is rare.
Note: Apparently some Canadian banks are not allowing Visa/Mastercard deposits to gambling sites. CIBC (for sure) and BMO (so they tell me) are still okay.