Measuring is super simple, just measure the distance from your transfer case yoke to your pinion yoke as shown below. Yes, the lengths can be fairly standard but a couple minutes of your time measuring will ensure that you get the right thing the first time around. You'll hear a lot of people say "center to center" when referring to drive shaft measurements. Center is a matter of perspective so it's important to clarify what that means, it's center of joint to center of joint, or centerline of the bearing cap. Measuring to the edges of the yoke as shown below will give you that number. The reason we tell people to measure from yoke to yoke is because if we tell people to measure center of joint to center of joint they'll often take the shaft out, lay it on a bench, and measure it. But because the shaft compresses and extends it is very important that the measurement is the "running length" the normal installed length.
From there, just make sure that whoever you order a shaft from understands how you ordered. I always say that there is not a right way and a wrong way to measure as long as we are both talking about the same way. There is no official industry standard for the proper way to measure drive shafts. Most companies will measure similarly to us though.
Side note: Someone previously said something like "Surely there's a Tom Wood's equivalent in Canada". Because international shipping is cumbersome and expensive I wish there was, just so our friends up north had more options, but if there is a similar company in Canada I haven't heard of them. I know of Pat's Driveline, and I know that there are some other local shops. At one point a few years ago I thought to myself, maybe there's an opportunity here, maybe we could set up a Tom Wood's Canada location or something like that. Then I realized that Canada only has about 1/10th of the population of the United States, making it a relatively small market. Which is probably why there are fewer options for Canadian consumers. We recently changed our international shipping policy, we no longer ship internationally because of the high shipping costs and higher rates of problems such as lost packages. We're leaving Canada open though, because I really don't want to further limit the options for Canadians.