What kind of coverage? Flight Delay will cover your expenses while delayed, but will not cover making your own onward travel arrangements which would presumably be necessary on separate tickets.
Provided the trip is insured by the card, Trip Interruption on Amex Aeroplan Plat covers 'delay of a common carrier causing you to miss your connection' which can be a train, bus, flight or anything else as an insured risk and will reimburse onward travel (in Y only) up to $1,500. However, general exclusions item 2 in the policy specifically excludes "any reward tickets except those purchased through Membership Rewards". (
https://www.insurance.americanexpres...ert-E-Se12.pdf page 21)