I think if the Germans seize Vichy France, with the western Allies having landed in Spain but not landed in or attacked French north Africa, then the French resist any German move on Tunisia or Algeria. Original timeline, there was confusion with the Allies 'attacking' French North Africa, Darlan dithering, and the Germans offering to 'help repel' the Allied invasion of French North Africa. As I understand it, the Germans started to get troops into Tunisia (ostensibly as allies) and with local Vichy approval on November 9th, 1942, a day or two before 'Case Anton' and the seizure of Vichy ruled France.
I can't see French pride allowing the Germans to gain a foothold in Tunisia if the western Allies aren't 'attacking' French North Africa and the Germans are in the process of (or have just rolled up) mainland Vichy France.
I don't know, if the western Allies are landing in Spain, if Germany could wait to try to get troops into a neutral-ish Tunisia first, either, before moving on Vichy mainland France.
So, I think, events probably proceed:
1) Western Allies land in Spain. Franco declares against Germany as soon as the landings (probably initially of planes flying off carriers to Spanish airfields, to cover troops arriving by boat/ship) arrive, and expels diplomats, gives appropriate notice to volunteers fighting in Russia of what to do, etc, etc.
2) Hitler rants and raves, about Franco's treachery, and about the importance of stopping the allies at the Pyrenees, at the very least. He sends a message to the Vichy government: German troops will be moving into the territory you currently control in a couple of hours time, irrespective what you do. Are you on our side or not? He possibly offers France Spanish Morocco, for what that's worth (if anything) as a 'bribe'. He also notifies Mussolini to be ready to move to seize southern France and Corsica.
3) The French are (most likely) largely unimpressed. Laval tries to negotiate with Hitler and Marshal Petain and to reconcile them, but fails. The German tanks start to roll. Darlan orders the French fleet (which has been fiddling with its fuel gauges) out of Toulon and to French North Africa. If he's not already in French North Africa at this date, he possibly accompanies the fleet.
4) Orders are given by Darlan to French North Africa to resist any German/Italian landings or attempts to bring troops in by sea or land.
5) Possibly Petain stays in mainland France, declining to leave it, and is captured by the Germans. In the meantime Darlan sends a message to Washington noting that between Franco's forces and the western Allied forces now landing in Spain, the western Allies have somewhere close to the 'if you come with twenty divisions, we will ally with you' figure (I think that with Franco it *probably* comes close to this) and asking if they would like to fight alongside France, and put forces (or equipment) in French North Africa to help repel any landing attempt from Italy and/or to attack Libya from the west? At the very least, the French fleet in North Africa needs fuel, to fight.
6) What next????