Well, Trump's cult followers are unreachable - whether in Pennsylvania or anywhere else. They're not the target.
But for anybody who lives in Pennsyltucky who has not bought into the Trump con game, Tim Walz will be very appealing. He's a regular guy; no Ivy League degree, no billionaire sugar daddy. He enlisted at age 17; went to college locally on the GI Bill, taught high school social studies for 20 years, coached the high school football team. If you're from rural Pennsylvania... he's your dad, your uncle, your brother. He graduated from high school in a class of 24 kids, served his country, and then made something of himself, by serving his community.
Kamala Harris' appeal will be more to urban people, and to educated suburbanites. Walz speaks to the working class. School lunches. Family leave. Housing. Basic stuff.
I love Josh Shapiro, but I have to think that Walz will be about as effective at reaching the undecided/independent voters of rural Pennsylvania, as well as Republicans who are sickened by Trump as Shapiro would have been. Beyond PA, Walz will appeal in Ohio, Michigan, Wisconsin, etc. Given the disgust with Trump, and the fallout from Dobbs, we may even find some typically "safe" midwestern red states in play, and that too is Walz' wheelhouse.