Make sure you use a backer rod for a proper result as they say in the Loctite page - not suitable for "Joint depths greater than ½" without the use of a backer rod". If you do not, the sealant may tear along the side or through the middle, but if it does the joint will still be mostly sealed off and it is not such a big deal for a garage unless you are wanting perfection. Joints are normally sealed after coating.
Backer rod is a round rod usually of polystyrene that is pushed down into the joint leaving about 3/8th inch depth for small joints - there is a chart of the depth vs. size of rod. You then apply the sealant on top and use your finger to smooth it out below the top of the concrete. It should stick to epoxy, but no guarantee.
Technically, you should cut the joint after epoxy coating with a diamond saw to expose fresh concrete, then apply a primer if necessary to the sides of the joint and then apply the sealant after the backer rod is inserted, but who the hell is going to do that for a garage? Just letting you know what is done in industrial applications.
The sealant has to squash when the temperature is high and stretch when the temperature is low because the slabs come together and spread apart with increases and decreases in temperature. The backer rod limits the thickness of the sealant so that it will stretch and it gives it a semi circle profile at the bottom and your finger gives it a roughly semi circle profile at the top. This gives the sealant the ability to stretch without splitting. If it is applied into the joint in a square profile top and bottom it will tend to tear and split when stretched. Polyurethane is the most common type of joint sealant.
An explanation can be seen at
http://www.sika.com.au/cmc/Datasheets/tds/SikaflexConstruction_tds.pdf and if you apply after coating be very careful not to make a mess.
Sealing joints sounds good, but it is a fiddly job.