Tandem by Anna Jarzab

Random House, 2014. ISBN 9780857982995.
(Age: 12+) Sasha is a 16 yr old orphan living with her grandfather until the night she is kidnapped and taken to a parallel universe. Her mission, which she must accept if she wants to return home again, is to impersonate Princess Juliana (her double or analogue). The real princess has been secretly kidnapped by revolutionaries just days before her marriage to a foreign prince. Sasha must stand-in for the princess, in order to prevent ongoing animosity and possible war between the United Commonwealth of Columbia and adjoining, Farnham. These kingdoms roughly equate to USA and Canada in Sasha's universe.
Her kidnapper, 18yr old Thomas who is a special agent back in Columbia, is also an analogue of her long time unrequited love interest on Earth, Grant. The unsuspecting groom, Prince Callum, forms a love triangle but Sasha's heart belongs to Thomas - despite being Sasha's abductor. Complications include a good many power struggles between a despotic General who rules through a comatose King, wicked Queens and revolutionary forces.
As far as parallel worlds go, plot and setting are detailed and credible enough to keep us turning the pages but none of the characters are particularly endearing or likeable in themselves or in their interactions. When the adventure ends for Sasha and Grant after a good many twists and turns, the fates of their analogues remain uncertain and this is reason enough for lovers of Sci-Fi to anticipate the sequel.
Deborah Robins