1. If Scotland were a Canadian province, they'd likely be a "have not" province and equalization payments from other provinces would go to Scotland. Good for Scotland, but this would be a drain on the rest of Canada.
2. If Scotland seceded from the UK and joined Canada, that would be one heckuva precedent for Quebec, which has held referendums on separation before. How Scotland makes the decision to separate (e.g. 50% +1 of a referendum vote?) would have a big impact on Canada, even if Scotland doesn't join Canada.
3. Like an unfaithful lover, if Scotland were to secede from the U.K., could they be viewed as anything other than a fair-weather province? Is it worth pouring resources into a province that's likely to leave later on if it suits them?
4. How would Canada-U.K. relations be affected by this?
5. How are military assets going to be handled? What does Scotland take with them, and what does Canada (not the biggest of military spenders) have to do to maintain Scotland's current military readiness? While I doubt the rest of the U.K. would pose a threat, they might not be happy giving up equipment, soldiers, and co-coordinating the defense of the British isles with Canada. It's fair to note Scotland would face all these problems if it goes it alone. For Canada, they are optional.
6. How are Canadian nation-wide services going to be rolled out to Scotland and/or harmonized with those of Scotland? e.g. Canada Post would suddenly have to deal with an overseas province. Flat rate shipping within Canada would suddenly cease to exist.
7. Contrary to what the article states, geographic distance is still immensely important. Integrating Scotland into Canada's economy would pose huge problems. Scotland would likely be better served with closer economic ties to the E.U.. Would Scotland want to abide by Canada's trade deals with the E.U.? Would Canada want to modify those deals to meet Scotland's needs?
I could go on for a while, but what does Canada get out of all this anyways? Haggis and scotch? Scotland has had a huge impact on Canada's culture, but that doesn't necessarily mean we should take them in as a province if there aren't compelling economic benefits to doing so. Becoming a larger country does have some appeal, but this is a case where the problems created may outweigh the benefits of growth.