Well the fact that Primera announced BHX STN and CDG at the same time may suggest Primera started planning well before United announced a pull out.
Icelandair could well be to do Primera likely to eat into their share of the market although there's was not direct.
As for Air Tansat not really a surprise, BHX became their only UK airport with just 1 Canandian destination.All the others having at least 3 destinations with UK crew bases.
In the end we will probably never know the the sequence of events .