Nexpress and Nexus are two different things. Nexpress is a fare card to pay the toll. Nexus allows you access to a dedicated Customs Lane. Here, using your same quote
On that same website you posted.
Click the Customs Link
When you have a Nexus card, you still have to stop at the border and talk to a regular human.
With that out of the way. Now, you are linking to getting a Canadian Permanent Residency. That is completely different from the visa system and also a million times harder to get into. In addition, we cap the number of people we grant permanent residency to. For good reason too. Permanent residency is essentially citizenship without the right to vote (and has residency requirements). You can not on a whim just decide you want to become a permanent resident. It requires years of paperwork, and actually living in the country under legal means (through various Visas) in order to gain the option of applying.
A Foreign Talent (defined as Not American or Canadian) that Amazon brings in to work in an HQ in Detroit HAS TO LIVE IN AMERICA. They can not get Canadian Permanent Residency. They can not get a Canadian VISA. They can not live in Canada. They can not work in Canada. If Amazon brought them in under an office in Toronto or Vancouver, then it's the exact same previous sentence, but replace every single "Canada" with "USA". If Amazon is hiring foreign talent, said foreign talent has to live in the country they are being hired into.
We are not the European Union. We do not have 100% Free Movement of labour. We still have Borders that you have to pass through and speak to agents at, however slack they may be. Canadians that work in the USA can do so because they either have obtained a Workplace Visa, they have a Greencard/PR/Citizenship in said opposite country. They can not work in the other country without one of those items.
Foreign Talent that Amazon would bring into a Detroit HQ would not be eligible for a Nexus Card. As a result they would have to use the regular border crossings. When doing so they have to show up with their Passport and Work Visa. They also get to play 50 questions with the border guard about what their purpose for entering the country is, how long they will be staying, how much they plan to spend and when they can expect you back. They note your answers to these questions in their computer system and they pull up this information and review it every time you pull up to the border window. You may also be asked to go inside to go speak to an Immigration Employee at a counter for further review of your paperwork if anything sparks the border guard into thinking something fishy is going on. Their systems are also automated to the point of telling guards to forward people inside immediately if it detects any patterns.
Now tell me. If a Person arrives at the Windsor-Detroit Border with a Passport from say the UK, and a Work Visa in the USA twice a day. Once at 9am going to Detroit and again at 5pm going to Windsor. And they do this every day for even a week. what do you think the border guard is going to do?
Remember, this person doesn't have proper permits to Live in Canada. Proper permits defined as a Canadian Citizen, Canadian PR, Canadian Refugee or a Canadian Visa holder.