I am filing 3 years of back taxes and I cannot continue because I need to know what my RRSP contribution limit is for that year, I need to find out if I have to wait till the government processes my 2014 taxes, to receive my Notice of Assessment or can I obtain this information somewhere else. Also I think I may have made a mistake on my 2014, will the government correct this or should I take it to an accountant and file an adjustment?
Go to http://www.cra-arc.gc.ca/menu-eng.html the official CRA website. Click the link to create a "My Account". The CRA will mail you a password to your address on file, which you will use to confirm your account details with them. This will give you automatic access to a lot of valuable information, such as past notices of assessment, plus copies of current tax slips they have on file for you.
There are two ways to file multiple years at once, and both of them you can do yourself [though if you are overwhelmed an accountant may help. Ballpark guess at a fee would be $500-$1000]:
(1) You can file everything at the same time, carefully calculating all of your carryforward information manually and placing it in your next year's return [really your software will do this for you]. If you do this I recommend you paper-file everything in a single envelope, with a covering letter indicating what you are doing ("Dear CRA, please find enclosed properly completed tax returns for tax years 2014, 2015, and 2016...") Advantages: can get processed quicker; the CRA sees all at once that you are trying to be compliant. Disadvantages: if you miscalculate something, your carryforwards will be wrong and your later years won't match CRA's balances on file for you.
If you have an incorrectly filed year and you also have some other years to file, you can correct your old year in the same file (search the CRA's website I list above, for "T1-Adj" form, which is a one page form that highlights the changes you are making to an adjusted return). Just put that one first, and again, indicate in your covering letter what you are doing.
(2) You can file one year at a time, waiting for the CRA to assess your old return before you file the next one. Advantages: by waiting for CRA assessments each time, you know that your carryforward balances are correct. Disadvantages: each response from CRA is going to take at least 4-6 weeks [processing times for old returns are much slower than processing during Jan-April for the correct filing year]. This means the process altogether might take you 6 months to complete.
But, don't take my word for it - search the CRA website yourself to get full details on how to refile your taxes: http://www.cra-arc.gc.ca/changereturn/