Deductions & credits

Dear sir,

 

I will appreciate your answer on my scenario.
I bought a Canadian property at $441k Cdn out of which we assume the land cost is 151k

 

It was my principal residence for 7 years, and I was renting out 20% (2 rooms) and living in the rest of the space.

I moved to the US and rented it out 100% for the past 3 years 

 

I have never claimed depreciation and am trying to catch up by filling out form 3115

 

At the time of purchase the exchange rate was almost 1:1, over the years the Cdn currency has been going down in value. So when I claim depreciation, do I adjust the cost basis for every year per yearly average exchange rate? Canadian value remains the same but USD would be going down each year since.