To answer this question, I need to clarify the basic concept. GMap is not an app that runs on either a smart phone or a Garmin GPS. It is a thing that runs on a server. When you view GMap you are viewing it in a browser. Mostly Gmap is used on your computer.
To see topomaps on your GPS when in the backcountry, you need a GPS App which runs on your phone. Once you have such a GPS app, you can download similar maps that you see in GMap onto your phone. The GPS app that I use for my android smart phone is Backcountry navigator. It costs about $15 one time charge. On a iphone, a typical app is Gaia, which is a subscription deal about $25/year. On my Garmin units, I use a package they call "Topo Canada" which cost about $100. It can only show very plain black and white topos due to the low resolution screen.
Once you have an App running on your phone, you can import overlay information from Bivouac which shows up on top of your topo map. The simplest is to download the track log for a single trip or trail. The method of transfer is a Gpx file. But with the smartphone you can also download a gpx file that contains all the bivouac road, trail and mountain information for a 20 km radius. (Or larger radius for selected items with GpxForm.)