Each holder is responsible for their own %, if the account is held in both names, then you enter in their percentage while keeping the other account holder's % as well as SIN#; for your record, in case the CRA asks for it later.
It will be allocated according to how you've claimed the type of ownership of the rental property as a "co-ownership/ sole proprietor" instead of "partnership". If you change this selection to "partnership", this will be allocated according to the percentage of ownership entered.
Please see link below for further clarification:
https://turbotax.community.intuit.ca/replies/2647946