Here's my two bits. I am a fish and wildlife biologist with years of experience in forestry and a lifetime of hunting/shooting and your problem is one that I deal with every day. I am usually 10 km away from my truck and a couple km away from my ATV so personal defence is important for me. In my cruisers vest I always carry bear spray and bear bangers but I never feel safe. I work alone in young forests averaging 40,000 stems per hectare so I don't see bears till i trip over them.
Bear bangers don't work at all, i will show up to a cutblock and lean on my horn for 30 seconds to a minute, walk into the forest and the bears are there, they feel safe as long as they are in the treeline. I find if i use a bear banger the bear runs away in the direction i need to travel (scary) and sometimes i see the bear again.
Bear spray is always good to have on your belt but you only get two three-second bursts out of a can. Last month I stumbled across a bear so I grabbed my camera for a pic and there was another fully grown bear within 20 meters of me. I only had enough spray to handle one bear and think of how often we see multiple bears together.
I usually walk around with an iPhone playing music in my pocket to make some noise and I wanted to pump it up a bit so I put big speakers in my back pouch. Big mistake, I have never been more scared of bears when I can't hear them coming! I now have bells on my vest at all times.
Now i carry an 870 express tactical with me at all times. I have an extended mag and I alternate buckshot and slugs in there. At first i used a sling but it kept catching on trees and i was scratching my stock and barrel. Using a sling it would be very slow to prepare for a charging grizzly, especially if i am wearing a helmet for the ATV because i would have to take my helmet off before i could get the sling over my head. I just put on a pistol grip and bought a sac for my back (gunny sac?) and it is GREAT! I can wear my cruisers vest over top of it and draw my short shotgun real quick anytime. also i don't have to worry about scratching my new gun or junk getting in my barrel.
As for Parks, make sure you check the hunting regulations for park specific details. For example, Sugarbowl Grizzly Den Provincial Park near Prince George BC allows people to carry firearms only during certain parts of the year.