Assuming he's on a published fare, it will be doable.

The way the agent will do it is - calculate the price of H, minus what you paid + $75 service/reissue fee = what you will have to pay. It will probably be around the $420 CAD including taxes.

He has to do it on tomorrow (Friday) given that he leaves next Friday. H7C carries a 7 days advance purchase.

AC127 on 08AUG has 10+ seats unsold at this point. AC140 on 10AUG is a bit more tight as there are only 8 unsold seats (and the upgrade window for SE on B or higher still hasn't opened yet). AC110 and AC1104 would give you a better shot based on the J loads now.

Both of those flights are dinner flights. The info I have is that the new J meal service has commenced on this route about 3 weeks ago. Although I've been hearing conflicting reports about this. I could find out for you if I have time.

Also, if I recall correctly, you've met the requirement for the Elite fasttrack? Your status might change over to Elite this weekend. If so, that will give you an even better shot at getting C (should you decide to upfare).

On the other hand, if this is a FUN fare, you won't be able to upfare it to H.