You can file tax returns for 2016 and the previous 9 years if you have not already done so. Certain credits including the GST credit will be paid retroactively, other credits such as CPP/EI overpayments and various provincial credits will only be paid for 3 prior years. You can use Turbo Tax to prepare your 2014, 2015 and 2016 tax returns online. And additional prior years with our software are available as a download.
https://turbotax.intuit.ca/tax-software/prior-year-taxes.jsp#2014
Older Revenue Canada tax packages can be found here.
http://www.cra-arc.gc.ca/formspubs/t1gnrl/llyrs-eng.html
