There is no link and no specific application. Visa application centres are supposed to review all applications to screen for CAN+ eligibility. If you have a valid US visa, you will automatically be considered for it.
The TRV application form is the same. If you apply online, you must scan your US visa (and any entry stamps) + specifically request for CAN+ processing.
If you submit a paper application then request VFS staff to mark your application for CAN+. You will need to also submit the passport that has the US visa