In Pepsi, your solvent is water & the solute is mainly sugar.
The bubbles come from the release of carbon dioxide gas that was dissolved in the drink.
A solute is the substance to be dissolved (sugar). The solvent is the one doing the dissolving (water). As a rule of thumb, there is usually more solvent than solute.
In a solution of two liquids, it may be difficult to say which substance is the solute and which is the solvent. In general, the substance present in the greater amount is the solvent.
Learn more about solutions and mixtures at Chem4kids.com.