You need a proper US board, consisting of mainly US residents, to do this, amongst other things. For example, if you’re a full Canadian company, with a top US holding (no operating income), that is fine. Also, if this is a VC setup, there isn't any money to be made, since you're making losses. Loss making companies aren’t really looked at, unless you're using those losses to offset profits somewhere else.
In the end, it’s all about ‘corporate substance’, google it.
I can set up a BVI company tomorrow, capitalise it with $5M, and use that to buy a boat - no one will care (in most cases).
You can’t just have a ‘shell’ create operating income out of thin air (in most cases). Who is operating the business then? IP holdings, internal corporate banks, etc, all that stuff is much easier to do without significant substance. But running a SaaS company, completely out of Canada, without paying some tax in Canada, will be hard to do I think. You could have a US company own all the IP rights, customers, and everything related to the business, and then appoint an ‘agent’ in Canada to operate the SaaS business, and pay them a fee for it, for example. It's better for the agent to at least pay some tax as well. But you still need proper US substance to that.
But you can bet, if you’re booking millions through a Delaware company that you’re just running from Canada, with no proper board etc, there is a real chance this gets challenged. That is, if they find out about it. Delaware might not be the best example, but if you replace it by a low tax jurisdiction (i.e. Cayman Islands, Jersey, Cyprus, etc), that gives you a better idea.
Because, face it, why wouldn't we all have a Cayman company then? :)
Also, different countries have different anti avoidance measures in place to combat this.