Valerie
All who served in the 1st WW would have received a medal(s). You mentioned the Canadian soldiers - was your grandfather Canadian as if so this would reduce the likely regiments. If not it will obviously be difficult. I think the army still use Kinmel for training and it might be possible to find out which regiments used the camp then. If not you may be able to write to all the different Regimental associations but these will have changed over the years. The internet may help.
Can anyone in the family help? Did he have any other name? Normally men served in local regiments although this is not always the case. I had a great Uncle from North Wales who served in a Yorkshire regiment!
If you paid the £3.50 I have a feeling it will only tell you what medals were issued although I am not sure of this and in any case you need to choose your best guess otherwise it will be a lot of £3.50's to spend.
It may be an idea to phone the National Archives if you can.
It may be worth looking at Cyndi's list UK military to see if there are any links which would help. See below
http://www.cyndislist.com/miluk.htm#FindingI don't know how else you can find out as the name is not uncommon enough.
Peterej