New Workouts to Maintain

Hello... I am looking to maintain my current weight and build some lean muscle. I am an 18 yr old male, 5'7" and weigh 150 lbs. My rountine for quite some time now has been running three miles and biking for about 20 mins a day. I have the opportunity to take some fitness classes such as spinning and other cardio and toning classes. The classes are usually about 45 min long. Would I maintain my weight if I started to substitute the classes for my current workouts.... or do these classes burn significantly less calories??? Any help or suggestions are appreciated!!!!

None of the exercises you're doing will build muscle. There is also no such thing as "toning"

You need to start weight lifting if you want to build muscle, and weight lifting burns fewer calories than cardio. 

But then again building more lean tissue through resistance training (weights) will burn calories in the long run because it will increase your metabolic rate.