If you are a person who burns readily then sunblock at all times plus long sleeve shirt and hat are your only answer.
However the danger of sun, IMHO is overrated, compared to the other hazards of life. At one point I used the World Almanac for figures: Fatal skin cancers kill about 2 people per hundred thousand per year. So skin cancer has about the same risk as getting murdered in a civilized part of the world, or about 1/4 that of being murdered in the U.S.
Given also that skin cancer risk is greatly increased if you have had even one serious sunburn, the risk seems to be associated with burning, not the exposure.
If you are more comfortable without a shirt, do so. If you have a sensible prep plan for a couple months ahead of time, you can skip the sunblock.
In passing: In 35 years of working outside and canoeing, I have ended up using sunblock on nose and ears, and occasionally full face at higher elevations.