First, is there any particular reason you’re stuck using Julia v1.2? That’s several years old at this point and basically unsupported - the current long-term support version is v1.6. Using an old version of Julia also prevents you from using modern versions of Julia’s CUDA stack - I’d highly recommend upgrading to at least Julia v1.6.
Julia’s built-in package manager supports environments by default, so you shouldn’t need any external package. Briefly:
julia> cd(mktempdir())
(@v1.8) pkg> activate CUDATestProject # enter Pkg mode with the ] key
Activating new project at `C:\Users\alexa\AppData\Local\Temp\jl_gcrbSw\CUDATestProject`
(CUDATestProject) pkg> add CUDA
Updating registry at `C:\Users\alexa\.julia\registries\General.toml`
Resolving package versions...
Installed GPUArraysCore ─ v0.1.0
[...]
julia> using CUDA
julia> @time sum(CUDA.rand(10^8)) # CUDA is downloaded at time of first use
Downloaded artifact: CUDA
145.488497 seconds (30.93 M allocations: 2.484 GiB, 0.50% gc time, 4.94% compilation time)
5.000604f7
julia> @time sum(CUDA.rand(10^8))
0.093087 seconds (145 allocations: 7.844 KiB)
4.9994404f7