I am sure you will have many answers for enzymes  but one problem is the high GC content. Running any pcr in presence of 1 Molar betaine is very helpful in making the melting of the high GC template much easier and making the pcr work with any polymerase

Thanks Paul

Q5 from NEB works well for high GC templates (https://www.neb.com/products/m0491-q5-high-fidelity-dna-polymerase)

Th phusion Taq includes a buffer that goes well for high GC content, and also is a high fidelity enzyme, that it would be more suitable for cloning after amplification

Q5 DNA polymerase worked for me for all high GC content template, follow NEBs supplied protocol and you will surely get good amplification.