If it's stuck in Customs, then they may not have a way to see what's going on or when it will get released, but I'm not sure if that's a possibility since I've never ordered something from the US shipped to Canada.
If your selected config which was not available in the local US warehouse your package will probably travel directly from China so it will take probably at least 2 weeks to get to you. On the bright side - you might get freshly manufactured device lacking issues that users reported in early days...
NOTE: I'm not Dell employee and even not North America citizen so this is only my guess.
Not necessarily - many systems are shipped direct from the actual manufacturer (which is not Dell) in Asia to you.
A decade ago, Dell did most of its own assembly - desktops and even configuration for notebook systems. That is no longer true - as with all the other "brand name" system vendors, the systems are shipped lock, stock and barrel from the ODM.
Dell still does some server assembly itself - but not for notebooks or desktops.