Imhotep didn't plan to put Anck's soul into Evy's body. He needed a sacrifice to complete the ritual. With Evy's death, Anck's soul would return to her mummified body and she would live again. I do think Imhotep recognized the princess or atleast noticed a similarity between Evy and Nefertiri.

I always assumed Imhotep accidentally triggered Evy's visions/flashbacks. He wanted Meela (Anck Su Namun) to remember but perhaps the spell was strong enough to reach out to Evy, making her relive the old days and her past life as an Egyptian Princess.