Yes, you can preselect a seat if you are traveling with a pet. However, for reasons of space restriction and security, you will not be able to preselect seats in row 5, nor in the Emergency Exit rows.
If your pet is a service animal, the passenger will be able to select row 5, however, due to government restrictions, you will not be able to select seats in the emergency rows.
In both cases, passengers will have the option of preselecting seats in the other rows depending on availability.
For additional informaton visit Advanced Seat Asignment section.