I'll tell you right away that there is no chance for me to answer without being very technical. Since you're looking for an open source solution it cuts away all of the commonly used programs and leaves us with a bunch of programs that require more from the user. The advanced part has nothing to do with photography though. The technicalities lies in programming.

Basic answer that could be what you're looking for

The program that I would use is gPhoto. It is open source and licensed under GNU LGPL. It allows for remote controlled configuration and capture, depending on the camera. A list of the supported models can be found here.

You also wanted the camera to be WiFi enabled and I'm most familiar with DSLR:s so that makes me think of the Canon EOS 70D and EOS 6D as well as the Nikon D5300. The D5300 is not on the official gPhoto supported list yet (although it might work fine anyway). The big problem here is that as far as I know there is no way to remote control these cameras wih gPhoto (or any other open source program that I know of) over Wifi - you need a wired connection. You were not clear regarding whether these were two separate requirements or if you wanted to use the WiFi connection to remote control it. If it is the latter I can't help you as of now.

Regarding the landscape photo aspect any of these cameras will do. The 6D has a slight edge being full frame and will give you a wider angle of view when using the same focal as the cropped bodies, but it's not a game changer.

Possible solutions if you want to remote control the camera over WiFi

If you can abandon the open source requirement and go for a closed source solution instead there are always the official Canon EOS Utility software (included with camera) or Camera Control Pro 2 (not included with camera) or third party options like Adobe Lightroom. They work on Mac, but not on Linux without you having to mess around a bit first.

If you are not prepared to deviate from the open source requirement I can think of one solution that will require a lot of skill from you. If you use a Raspberry Pi and hook it up to the camera by USB you can remote control it using gPhoto. Then you can attach a WiFi dongle to the Raspberry Pi and then use an SSH connection to remote control the Raspberry Pi using a command line interface from any computer that has an SSH client, running Linux, Mac or whatever. You have to solve a few problems such as powering the Raspberry Pi and accommodate it somewhere while using it with the camera. Photographer David Hunt actually wrote a guide about how he fit a very similar solution inside his battery grip to his Canon 5D Mark II. I know that this last solution is very advanced indeed, but it's the easiest one I can think of that satisfies all your need if you also want to remote control it over WiFi. Note that this solution doesn't require you to use a WiFi enabled camera since the Raspberry Pi enables this for you.