If I bought my own iphone directly from Apple ( 32 GB,s)

. How to use it with Roger?
And how much it cost per/month for the plan? Is it different cost than if I pay from Roger with a 3 year contract?
The main thing is: Im not a Canadain and I will stay there only for 2 years, I don't want to lose money & I want to use it when I get back Home too.
Please let me know , what are the best choices for me with paying an Iphone?


Thanks!