First, highlight both tracks. In the Effects menu, choose Amplifier > Normalize. In the Normalize dialog box, set maximum amplitude at 0dB. This will amplify both tracks until their loudest peaks top out at 0dB.
If one of the tracks has a lower nominal volume than the other but also has high peaks that prevent it from being amplified to the same nominal volume as the other, then you must first use your compressor or hard limiter to lower the peaks on that track so they are similar in level to the other's peaks. This must be done before either track is altered from its original form. Then, you follow the steps in the first paragraph to amplify them to 0dB.
If this is unclear, don't be afraid to ask more questions!