Yes they're similar to /ga/ and /ka/ in English, the difference is that the g sound isn't a voiced sound, it's an unaspirated k sound (basically a k sound but restrained so there's no accompanying puff of air, and without the vibration that goes with a g sound in English). So English background speakers of Mandarin often sound heavier when they pronounce g/d/b sounds. I say this as an English background speaker myself.
Does mandarin have a significant difference in pronunciation between <ca> and <GA>?
Yes they're similar to /ga/ and /ka/ in English, the difference is that the g sound isn't a voiced sound, it's an unaspirated k sound (basically a k sound but restrained so there's no accompanying puff of air, and without the vibration that goes with a g sound in English). So English background speakers of Mandarin often sound heavier when they pronounce g/d/b sounds. I say this as an English background speaker myself.