As a resident of the Canadian portion of Cascadia I'd be in favour of a European style union of your former states and Canada. Unfortunately you're too big and too American (for lack of a better term) heavily armed [found it] to just let you in. Maybe we could handle Hawaii but I'm sure they'd probably rather be their own country than join us which is totally fair.
I wouldn't, as Canadian, because California would fully dominate such a union. It would be Canada joining California, not the reverse. Economically, politically, you'd be the biggest and most important province. I doubt you'll be happy being part of Confederation or being technically a monarchy.
Conveniently, if any states were to join Canada, they would most likely do so as territories (at least initially), and so would be somewhat politically neutered.
Honestly, Cali is already at war with the US. The current administration is already talking about withholding all kinds of random shit for cali. That sounds like an attack to me.
Trump has already drained some reservoirs without consulting experts, plus ICE is on the prowl. California is going to feel serious pain come harvest season.
Inspiration for a sequel. After Trump and friends are spending time at Mussolini's, we will need to make a whole new government. Having a blueprint for making a better Constitution will be helpful for making the rehabilitation process.
He died before he could see Reconstruction through, and his successor killed it.
Mind, Lincoln should have mass executed all significant leaders in the south. Offering mercy to those of a Nazi bearing always ends up damaging society. Better to put them down, rather than letting the infection fester.