Kanchipuram is small enough to navigate without much difficulty, but the major temples are spread across several kilometres and not conveniently walkable between each other in the heat.
Auto-rickshaws are the standard way to move between temples. Drivers outside the bus stand and train station are accustomed to tourists doing the temple circuit and will generally propose a fixed price for a half-day tour covering the main four temples. Negotiate before getting in; the going rate varies but is modest by any international standard. Ensure the price is for the vehicle, not per person, and covers waiting time at each temple (you'll need 30–60 minutes at each).
Cycle rickshaws are available near the bus stand for shorter hops in the town centre. Slower than auto-rickshaws but good for the morning markets area.
Walking is practical within individual temple precincts and in the town centre between Kamakshi Amman and Ekambaranathar (about 1 km apart). For Kailasanatha Temple, which is further west, you'll want a vehicle.
Hiring a guide: The ASI-managed temples (Kailasanatha, Vaikuntha Perumal) have licensed guides available at the entrance who know the architectural history in detail. For visitors with a serious interest in the Pallava period, a guide transforms what you see. For the active pilgrimage temples (Kamakshi Amman, Ekambaranathar), a local guide can navigate the inner precincts and explain ritual significance that wouldn't otherwise be apparent. Agree on a fee before starting.