We are going to open up a load-bearing wall in our 1 1/2 story house. The opening will be 4 m and the recommended beam size is 90x315. In my opinion, that beam seems too high and the question now is if I can use 2 beams with the dimension 56x225 instead? 
Spontaneously, without having calculated it, the answer is no. It is the height that accounts for the bending strength. Thus, a 112X225 is significantly weaker than a 90X315. If the height is so crucial, I would recommend you look at a steel beam instead.
we did exactly what you are planning to do, opened about 3.5 m, used 90x315, initially thought it would "divide" the room and be ugly, but now it's there and it's completely OK... you need to raise it to the floor beams on the upper floor so you can't measure directly from the ceiling to see where it will end up... instead, measure from the beams down.
and it's the thickness that gives strength, not the width of the glulam.
and it's the thickness that gives strength, not the width of the glulam.