If you apply through a registered patent agent, the agent can take care all the requisit paper work. What you will need to do is to sign a form that authorizes the agent to act on your behalf, to educate the agent what your invention is (face to face meeting or in writing), and to pay service fee in addition to government fee.
If you have decided to apply through a patent agent, you should get the agent involved as early as possible in the application process. As one has pointed out, Canada has a first to file system. The defects in an application as originally filed may not be cured by amendments even if an experienced agent is involved later.
Don't know where you want to apply, US or Canada, or both. If you plan to apply in Canada, you should get a Canadian patent agent who is normally also authorized to practice before the US patent office for filing a US application for Canadian residents. A US patent agent cannot help you for filing a Canadian application if you are not residing in US.
You may tell us where you are now in your application and how much you plan to spend. Those information are important in terms of offering advices on how you should proceed.
Hope this helps.