I think this is a decent fight between two fairly evenly matched fighters. Jack Brubaker is a solid domestic fighter and Steve Spark is the same.
Jack Brubaker has stepped up in competition in his last fight and was quickly stopped by Tim Tszyu but theres no shame in that as Tszyu is a quality fighter and Brubaker stepped up a weight class for that fight. Brubaker has some decent boxing skill but isn’t a big puncher.
Steve Spark is a decent boxer who has done very well at domestic level so far. All his wins come by knockout and he seems to be a very big puncher.
I think Steve Spark will likely win by knockout though Brubaker could out box him and win a decision if hes at his very best.