The obvious way to access the other side of Vice City is to do the missions. You might say not to say that in your topic description but you have to. What other way do you imagine you can unlock it?
Edit: To answer the other part of your question, the mission that unlocks the west island is called Phnom Penh '86. If you're looking to unlock it faster, don't to the Avery Carrington missions because they're not part of the storyline.
Now, hug me brothah! *Crowd Cheering*
Hey, Miley, I made you a cake. *Crowd Laughter*
Pathetic. Hey, Miley, I made you a shirt. *Crown Laughing and Hollering*
No avatar for Silberio.
Back to the random spam... This jacket? Well, there's only one way to get one... to be [Warp Sound] the President of the United States. *Crowd Laughter*
I agree, this is as too early to talk about as some topics about the PS4. There's likely to be a GTA IV trilogy like the GTA III trilogy so what's the sense in talking about GTA V at this time?
In the guide I used, they recommended a Barracks OL even though I didn't use one, I'm sure I used a regular four door car and killed him at full speed.
If you still have the bulletproof Barracks OL from Arms Shortage, then it's better to use that since the police can't do much to it.