Could someone please help me identify this bicycle? I cant find anything that looks like this on the internet. The reason I'm asking is because it needs a new seat, as the plastic has broken off from the metal post. Any information would be really helpful, even if you just know where to get its original seat.
Its a Giant Sedona, probably from the 2000's.
But that information is not very useful for replacing the saddle. If you look up underneath the saddle, there will be two parallel rails, and the seatpost clamp holds onto them.
The exact clamping method may be one bolt, two bolts, or a pair of nuts on a common axle. Regardless, undoing will allow the saddle to come out and a new one goes in the same way.
Aim to get the new saddle level and about the same distance back from the handlebars. Tighten and test-ride.
The risks are if the saddle moves while riding, it may surprise you. If saddle is out of position it may cause aches sooner. If the saddle's too soft it will compress and put pressure on delicate parts that cause aches. Your old saddle looks to have some thick cushioning or a cover on it.
There is absolutely no need to have the original saddle unless this is a showpiece bike. A saddle is one of the three contact points your body has with the bike, and it must be comfortable for you.
The stickers tell you it's a Giant Sedona. To me it looks like a fairly old model (they still make a similar hybrid under that name, but with suspension).
But you don't need the model details to replace the saddle. You probably can't get the original as a spare anyway.
Instead you need to buy a saddle that suits you (which might look a lot like what you're used to). I can't tell from your photo, but others I can find suggest it's a standard saddle with rails running front to back for adjustment, and a clamp at the top of the seat post. Do check because I've had bikes of similar style and age that used a different saddle attachment with no rails and the clamp built into the saddle. They're harder to find.
In addition to the fine answers provided, your question mentioned that the "the plastic has broken off from the metal post." This metal post is called a seatpost.
In the chance that the seatpost interface that connects to the seat is unique/proprietary (or that it is broken) such that it does not allow a standard two-rail saddle to be mounted, the seatpost (the post that connects between the seat and the frame) can also be replaced to allow mounting a standard two-rail seat. Although expensive seatposts are available, relatively inexpensive and fully functional seatposts are common as well.
The key parameters to match up a new seatpost would be the diameter of the seatpost (there are several different sizes), the length, and the setback position.
The diameter can be easily measured, and sometimes is actually stamped into the seatpost (visible after removing the seatpost). Similarly, the length is also easily measured when the seatpost is removed. If a seatpost is too long, it can usually be shortened. Finally, the setback position is the position of the seat clamps on the seatpost relative to the centerline of the seatpost. Typically, the position is slightly (1-2 cm) rearward of the centerline of the post, but positions on the centerline and forward are also available. These differences are used for customizing the riders' fit on their bike. Your local bike shop can easily help with this, if necessary.