I hate to piss all of ye off, but the line should be "It is so large it technically shouldn't exist, according to current astronomical
theories". It doesn't have much to do with physics theory.
And Canis Majoris is a dying star, becoming a bloated star if you like. It's original size would have been a lot smaller. Our Sun will eventually grow in size that will be the equivalent of Arcturus, giving it a radius of some 90-95 million miles, (one astronomical unit), although it's mass will remain roughly the same. CM is about 8 or 9 astronomical units at the moment. It's big, really fucking big, just not as big, relatively speaking, as is portrayed. It's not a like-for-like comparison.
Oh...and we'll most likely end up "orbiting" inside our star. Mercury and Venus will for certain.