NYC - If both Downtown and Midtown become unusable, would move it to DT Brooklyn
Boston - Would move it to Southie
Philadelphia - Move it to south Philly. Utilize all that empty space by Schuylkill and Delaware River
Washington DC - Easy, just move it across the river into Virginia
Montreal - Move it to Laval or the southern portion of the big island
Quebec City - Move it to Ile de Orleans
Miami - Relocate it to Fort Lauterdale
Chicago - Build it...just build it as far away from Indiana as possible. Maybe Waukegan
Seattle - Build it on one of the nearby islands (Bainbridge?) and make it super dense. Like another Manhattan