Try the following: it should land you in a page where you have two choices - Open Work Permit and Temporary Resident Visa. You should click on the latter to proceed to the TRV.
Doesn't matter that your form will be "TRV from Outside Canada" even if you are within Canada; it's a generic form.
What would you like to do in Canada?
Work
How long are you planning to stay in Canada?
Temporarily - more than 6 months (or Permanently) <- doesn't matter
What is your current immigration status in Canada?
Worker
Does one of the following apply to you? I am subject of a removal order that is unenforceable I applied for a study or work permit before entering Canada which was approved, but not issued at a port of entry; or I applied for permanent residence to an office in-Canada and was determined to be eligible for permanent resident status (first stage approval).
Yes
Are you are a spouse, common-law partner or dependent child of a person who: Holds a Work Permit for a job in National Occupation Classification O, A, B; Holds a study permit and is a full-time student at a university, community college, CÉGEP or other authorized educational institution; Holds a Temporary Resident Permit that is valid for six months or more; Applied for Permanent Residence to an office in Canada and was determined to be eligible for Permanent Resident status (first stage approval) Is subject of a removal order that is unenforceable.
No
Are you a spouse, common-law partner or dependent child of a person who is: a foreign government officer in Canada on an exchange agreement a military personnel assigned to Canada a participant in professional sports activities or events an employee of a foreign news company a religious worker
No
Have you been told by a Citizenship and Immigration Canada office that you are approved in principle for permanent residence in Canada?
Yes
Have you submitted a permanent resident application in Canada?
Yes
Do you have a written job offer?
No