Daisy reins are primarily used on ponies which like to snack when out on a hack with a tiny person on board, who doesn't yet have the strength to prevent the snacking.
They should not be used to solve a bucking issue, it isn't safe. A horse that shows adverse behaviour, in this case bucking, is trying to tell you something. If you try to restrain the horse you could make him feel trapped and in this situation, being a flight animal. he may panic, fight harder and really give you the full works.
You have to look into possible causes and work your way through them. You must be honest with yourself, if you are not then you will only be fooling yourself and not sorting out the issue. When does it happen only in canter ? Has it become a habit ?
As you can appreciate we do not have much information to go on so in general some things to think about are listed below;
1. The usual culprits; teeth, back, feet
2. Discomfort and pain from the bit
3. ill fitting saddle
4. ill fitting bridle
5. management - stabled for too long, feeding regime is not correct for the workload so he has too much energy
6. they way you ride, if you make him uncomfortable he will want to get rid of the discomfort. Are you hanging onto his head ? does your lower leg creep back ? are you tipping forwards or back etc
7. You may be asking your horse to do something he finds difficult or doesn't understand
Eliminate the obvious causes of discomfort first. It may be worth trying the canter on a lunge first of all to see what your horse does without a rider.
If the horse isn't comfortable then he will not give you his best.
all the best