Are you a Californian? I don't recall the US having an initiative process. Border security and employment law are not being enforced by a Republican president - do you think a Dem will be any better?
Annexing Mexico, however, is so far beyond the realm of the possible
There will be political union with Mexico sometime in America's future - and long before any illegal is ever sent packing. It may not be annexation, but it will be in effect an open border. No different from how it is now, in fact, but at least it will be a 2-way street and the US will get something out of the deal.