I was wondering if there is any other support for this besides that which I read on a notoriously unreliable online encyclopedia, that Mariana Vittoria, between being rejected as a future queen of France and becoming the future queen of Portugal, was actually proposed (by who?) as a wife for Pyotr II Alexeievich, Czar of Russia.
I know Pyotr II's mother didn't convert from her native Lutheranism, but she had to agree in the marriage contract that her children would be raised Orthodox. But Mariana would've been Catholic - and Empress Anna Ivanovna tormented one of her courtiers when he married a Catholic - and needless to say, I can't see the Pope granting the dispensation necessary.
However, it would be interesting. Might the Spanish Bourbons then have a different son of D. Felipe V if their OTL double-marriage policy goes through, since that would marry Fernando VI or Carlos III to Natalia Alexeievna. (After all, all of Felipe V's children were part of double-marriage schemes - originally D. Luis I & D. Carlos III were to marry two daughters of the Duc d'Orléans; then when that fell through D. Carlos III and D. Felipe were to marry the heiresses of HRE Karl VI (Maria Theresa and Maria Anna); and when D. Carlos III finally married Maria Amalia of Poland, his sister Antonia was to marry the Crown Prince of Poland; also, with the Family Compact, D. Felipe and D. Maria Teresa were married to the Dauphin and Madame Premiere respectively, and D. Fernando VI was considered for Madame Seconde).