Hello from Kelowna, BC! I'm including links to Canadian retailers for the harnesses I'm going to recommend. The Canine Equipment products can be ordered through most pet stores in Cansda (if they don't already have them in stock).
First, I'm a bit surprised at how many restrictive harnesses are being recommended. I must admit this issue caused quite a bit of confusion for me as so many people told me that thier cross chest harness was high enough not to restrict the dog. While this can reduce restriction, the truth is that any harness with a strap that goes across the chest will restrict shoulder movement. A wonderful vet pointed me to
this video from Muzo Training - it does an excellent job of illustrating the issue and clearing up any confusion about exactly where a harness should sit for the safety and comfort of the dog.
Secondly, please keep in mind that any harness can be backed out of. Your best single option is, as others suggest, is a quick release martingale. They have a clip so that it can be adjusted to the correct size and yet easily taken on and off. If you use a martingale, please be sure it's correctly positioned to protect the thyroid and trachea as best as possible.
On that note, you may wish to use a well fitted harness in combination with a martingale. You can use a dog coupler but a double ended leash will allow you to indepemdently adjust tension on the two restrains. The two harnesses most recommended by chiropractors and orthopedic vets as being non-restrictive of shoulder movement are the
Blue-9 Balance Harness and the
Perfect Fit Modular Harness.
The
Perfect Fit is a little more difficult to order as it comes in three seperate pieces. It also gets dirty more quickly due to the fleece which attracts grass, burs, etc. That said, some people really like the padding for dogs prone to irritation from harnesses (shelties have a dense enough coat that this isn't usually a problem). If this is what you decide to go with,
Dr. Dubias in Vancouver, BC takes orders.
The
Balance Harness is simple in design but very well made and adjustable on every strap so that the correct size is easy to determine and fit. Blue-9 also sells the
Multifunction Leah which is a double ended leash that doubles as a hands free leash (so it's something you can still make good use of after the reactivity has been dealt with).
Both these harnesses are non-restrictive when sized correctly, have front and back attachments D rings, and come in styles that clip around the dog vs going over the head (great for dogs that are head-shy).
After trying over 50 different harnesses and spending litterally hundreds of dollars, I finally settled on the
Balance Harness for exercising my boy in. If you contact Blue-9, they will send you a list of retailers in your province. I ordered mine from
The Bone & Biscuit in Grand Prairie, AB. Due disability, I still use our Comfortflex harness for quick potty breaks as it goes on so easily but it is restrictive and definitely easy to back out of. The only other harness I use is a
Sleepypod Clickit Seatbelt Harness to keep my boy safe every time he gets in the car. It is restrictive due to my boy's narrow chest and the limited adjustability of the harness (which also is what makes the harness such a good safety device) but some dogs wear them well.
For Martingale collars, I like the
Canine Equipment Quick Release Martingale. It avoids the need to readjust the collar with every use, is easy to remove in case of entanglement, and again clips around so is comfortable for dogs who are head-shy. The
Canine Equipment Beyond Control Leash is the matching double ended leash for this collar and one of my favorites. As a fellow Canadian, I like that this company is based in Vancouver, BC
