You can use Represent a Client to upload the RC59, although they would prefer the client sign the authorization in the CRA format that is included in the Represent a Client routine.
Log into Represent a Client
At the Welcome (Access Client Information) Screen you would scroll down to Administration (click on Review & Update). Under your Repid or Business (depending on your Rep a Client Access) click on your Repid name or business name, then under “Business Clients” select Authorization Request, then “Add Authorization Request”. Complete the information and have the client sign.
Once the Client has signed the form you go the same area, where it will show the pending authorization request. You scan and upload the sign consent form. Generally, after a few days you will have online access if everything checks out.
Alternately, the T2 module will allow you to Electronically File the RC59.
Since your client is not a Corporation, you can fake out the software, by putting the Client’s business information into the appropriate areas and electronically file the RC59. I have done this on a few occasions and find that it works well. After Electronically filing the RC59 you gain immediate access to the clients business accounts through Represent a Client. A word of caution with this, the information you submit needs to exactly match with what the CRA has in their records, or else your RC59 submission will return an efile error and you must try again.
Here is part of a discussion on this.
Here is some info on Electronically submitting the RC59 in TaxCycle