Vidkun Quisling was a man of fixed, if unpleasant, political convictions. I doubt whether he would have had the moral elasticity to act for British occupying forces as he did for the Germans.
With regard to "mainland France", read what is referred to as "Vichy France" in most postwar works. There were those in that regime who would collaborate with the German occupiers, only to whatever extent would mitigate the worst effects of the occupation. There were also some outright far right-wing sympathisers (such as Darnand, the Minister of the Interior) but far more many trimmers and time-servers.
A declaration of war against Britain by the Vichy government would not have been supported by the bulk of the French population, regardless of actions by British forces at Mers-el-Kebir (and later at Dakar, and in Syria and Lebanon).
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My personal distaste for right-wing sympathisers relates mainly to their flawed revisionist logic. For example, you occasionally hear some people referring to the "American occupation of Britain in World War II". In a very narrow sense of logic, the presence of US troops in Britain can be compared to that of, say, German troops in Hungary, in that in both cases, the foreign troops were invited by an indigenous government by treaty or agreement with their more powerful allies.
However, this puerile logic fails when the results are compared. Numbers of population forcibly dispossessed, deported and even murdered by the "occupiers" ? In Britain, none. In Hungary, several hundred thousand Jews, along with gypsies and slav minorities.
Other acts detrimental to the host nation ? Property looted, women raped, natural resources plundered, citizens executed for overt or concealed hostility to the occupiers? In the entire war, there were fewer than two hundred serious crimes reported involving American (and Canadian) soldiers stationed in Britain; and considering the numbers which at various times were stationed in Britain, this is remarkably low. Land might be temporarily requisitioned for military buildings; it was handed back when no longer required. Whatever amenities or facilities were diverted to the "occupiers" was more than compensated for by generous donations of goods and materials.
And so on. (And however galling it may have been at the time, I will not regard seduction by nylons and Luckies as any form of coercion.)