I have a 10 year old german shep. He started having trouble in his hips a few years ago. A customer where I work suggested a food called "Hills Science Diet Healthy Advantage". It's not the regular Hill's Science, u can only get this one at the vet, it's an actual prescription kind. Since we put him on that he has done GREAT! Runs around like he's a puppy, so glad we made that choice. I'm not sure if they would have this in your area, might ask around. Hope that helped some :)
woohoo fellow Canadian! Maybe I am down the street from you...Im in Markham.
Back to the question...first off can we be sure it is arthritis. Certainly lameness and leg pain in older dogs is most often caused by degenerative joint disease and arthritis occurs however there are many other possibilities. A confirmed diagnosis always improves treatment outcome. You mentioned when your dog gets up afetr lying down his starts to limp? As a general rule (dont bet on it but the odds are in your favour) when I see lameness after rest I think of soft tissue injuries. Just like with us when we have pulled and tight muscles once we get up and move around we feel better. Arthritis is usually the opposite. When we have rested it feels better but as the day progresses, so does the pain.
Lets say for arguments sake though that it is arthritis; the verdict still is not out on glucosamine in dogs. Their digestive systems are different enough compared to humans that we worry the glucosamine is not absorbed well. There are several great foods that your vet can recommend that actually reverse arthritis plus these foods are designed for senior dogs (less protein, higher fibre, more anti-oxidants) anyways and help prolong life. The daily cost of these foods are actually less then a good petstore brand plus supplements.
If you are really concerned, a second opinion is not unreasonable. Once a diagnosis is made then you may be able to benefit from acupuncture, physiotherapy, or even good old fashion anti-inflammatories and rest until the condition responds.
Good luck.
Cliff