を予約したいのですが

I'd like to book

→ を
phrase Rare #37,293
I'd like to book A polite way to say that you would like to make a reservation, often used when asking for assistance. The noun before を specifies what you want to reserve.
JA: ホテルの部屋を予約したいのですが。
EN: I'd like to book a hotel room.

バンクーバーまでフライトを予約したいのですが

I'd like to book a flight to Vancouver.

明日のディナーを予約したいのですが

I'd like to make a reservation for dinner tomorrow.

この列車の座席を予約したいのですが

I'd like to reserve a seat on this train.

を予約したいのですが

I'd like to reserve a table.