Hello, 

From the CRA website, looks like you need to use the Exchange Rates page of the Bank of Canada Web site:

http://www.cra-arc.gc.ca/tx/ndvdls/fq/xchng_rt-eng.html

I would use this page to calculate the yearly average (or if you needed the rate for a specific day or a specific month.): http://www.bankofcanada.ca/rates/exchange/monthly-average-lookup/

Have a good day!