Well it is all about pressure. If you have a VERY VERY STRONG container and at the Earth's surface, fill it will soda and a little air and then seal it, the pressure of the fluid in the can will be about 1 bar pressure.

Now if you put that can in a rocket and send it to say earth orbit, take the can out of the space ship and think about the situation before opening, this is the case:

We have a fluid at 1 bar pressure in a strong container (i.e. a container that can support the pressure difference, what is the pressure difference? Well it is zero pressure in space and 1 bar pressure inside the can PUSHING OUTWARDS IN ALL DIRECTIONS BUT NOT STRONG ENOUGH TO BREAK THE CAN.

Now what is "1 bar pressure"?
Well in the SI system of units 1 bar pressure equals 100,000 Newton/square meter, that says that there is a FORCE of 100,000 Newton per meter squared.

Now the surface area of a can of soda is 2*pi*R*h where pi=3.14, R is the radius of the can (about 0.03 meters and H is the length of the can, about 0.1 m.

To this we need to add the area of the top and bottom which is 2*pi*R*r...so, roughly let us say that the area of the can is 0.03 m².

Then the FORCE acting on the walls of the can OUTWARD is (100000)*(.03) =3000 Newton. Just for a comparison, the force i exert on the earth when I stand on it is about 800 N!! So you can see although it sounds like not much there is a large force (pressure is simply the force per unit area) that the fluid in the can is exerting.

So when you pop the can, there is going to be a large unbalanced force and the fluid is going to expand, the CO₂ that is dissolved in the soda will come out of solution and expand along with the liquid itself... there will be a small explosion and you will end up with a mess!!!

This discussion neglects temperature and other factors... but the essence is that the pressure will try to equalize to zero, the ambient space background and THAT means the fluid will EXPAND.

The answer to this question depends on whether you open the can in a pressurized spaceship, or outside the spaceship. If you were to open the can inside a spaceship the only real difference would be the absence of gravity, so the liquid would be free to float out of the can. Most likely since the can is pressurized the soda would be spayed from the can when it was first opened. If instead, you tried to open the can in free space, assuming the can didn't explode before opening, opening the can would case the pressurized contents to be sprayed at extremely night speeds and you would have nothing left in the can.

Water boils instantly in contact with a vacuum, and because most of the mass of a soda is water, it will immediately go into a boil. This will of course release the dissolved carbon dioxide in the water as well. It would look like opening a can of soda after it had been shaken up, only a whole lot more.

I'll guess the soda would vaporize and push the can in the other direction.