In my experience when reserving a hotel stay online, I would reserve a regular room. Then near the end of the reservation, they have space were you can input additional comments. I note the request for a room upgrade to a Junior Suite. Sometime within a week from your stay, Marriott will send a reminder e-mail about your trip. You can also make a request at that time when it indicates any additional services needed. When I reached Gold and Plat Status, I received an upgrade to a Jr. Suite numerous times.

One of hotels that usually grants this requests to me is the Crystal Gateway Marriott in Arlington, VA. I just had a stay this past weekend; I was upgraded to a Jr. Suite. Some of the reasons could be frequent trips to this hotel for business and personal leisure. The staff knows me by name so I am able to get my request granted each time.

The Charlotte Marriott City Center has upgraded me the last few times. About a month ago, I received an upgrade to an Executive Suite; a year ago, I requested an upgrade to what I thought would be a Jr. Suite, but I believe I received and upgrade to a much larger suite. The room had a large executive business table, 1 1/2 bathrooms, a living room sofa area that could seat 20 guests, and a bar table area.

The RI Midtown Atlanta on West Peachtree Street upgraded me from a Studio Suite to a one bedroom Suite.

Sometimes the rooms may not be available if the hotel is having a convention/conference in the hotel which may limit your upgraded room choices.