I had similar issues with my old British Eagle and a Pelago rack.
Had to gently persuade the fork mount, and use unorthodox bolt/spacer combo. Ended up ditching the cantis in the end as they fouled panniers when clipped to the sides.
I’ve ordered a longer bolt which will clear the canti straddle. I’m not sure if having a bolt that long introduces any issues in terms of how much weight it can bear though. I do have my vague plan of putting disc brakes on this though, which would solve the issue anyway.
I had similar issues with my old British Eagle and a Pelago rack.
Had to gently persuade the fork mount, and use unorthodox bolt/spacer combo. Ended up ditching the cantis in the end as they fouled panniers when clipped to the sides.