The limit is specified under the CDIC Act. It's currently around $23 billion. It is indexed to the growth of insured deposits, so it does increase over time.
Then, there's the Financial Administration Act, which has separate powers related to the minister's ability, for example, to lend money where he considers it necessary to promote financial stability or to maintain the efficiency of the financial system.
Currently the minister could lend money under those existing powers to CDIC. However, that money would count towards CDIC's borrowing limit. There may be circumstances where, with sums of money going from the minister to CDIC, the government may not want that money to go towards CDIC's limit, or there may be large amounts of funds.
CDIC's mandate includes paying out deposit insurance and also being the resolution authority for its members. It can use its powers and its money to fulfill those functions. This would allow more flexible, more timely, money to flow from the government to the CDIC if the minister and the Governor in Council deem it appropriate.